**The posts below follow my train of thought and actions taken. Never took it to a dealer, only used a cheap Bluetooth ODB scanner from Amazon. Wasn’t planning to dive that deep down the rabbit hole but sometimes thats the way it goes. Thanks to all the users for all your help and ideas!!

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Recently bought a ‘15 Fit Ex mtx with 130,000 miles. Service records show many oil changes and a set of front brake pads.

Have P0300, 0301, 0303 misfire codes with CEL ON. Feels like it runs fine and mileage is fine. Cleared the codes and after ~50 miles came back with exactly the same codes.

Plan on replacing coils and spark plugs. Coils with OEM from Honda (aftermarket Hitachi sold out everywhere)

My ? Is Would you recommend a valve adjustment? I have the Chilton procedure for the 2015 Fit valve adjustment and Ive seen the “KoolKevin1107” YouTube video of the valve adjustment process for an earlier model Fit, has anyone done a DIY for the 2015-up Fit?
Any major deviations?

The 15 model year had a tsb for injectors + fuel line replacement. Some 15's also had coil plugs recalled. Since your car has high mileage, it's hard to say what it might be. Spark plugs are due at 100k miles, along with valve adjustment.

Wishing you good luck with your troubleshooting. If the car runs solid and fuel economy is good, then maybe it's better not to bother with throwing parts at it and just drive as is? just an idea.

Replaced coils and plugs today. Plugs were black on the ends, also had some rust? on the ceramic.

Also adjusted the valves, many of the valves were tight. It was kinda scary opening the valve cover but went back together smoothly and fired right up after the 3 hour wait period.

One Note: I set the intake off to the side while working on the valves and noticed a puddle of oil on the ground underneath. Looked like about 1/2 a cup.
Only negative is the valves were gummed up pretty bad. Looked like 1/8-1/4 inch in places. Will have to look into a cleaning in the near future.

Wish I could have taken a good pic of the valves but couldn’t get the light inside the cylinder.

someone had trouble accessing the plugs. No photos there, any idea what the other OP was talking about? Any special Honda specific tools needed? I know I could go check for myself, but since you're posting and I haven't seen anyone else mention changing plugs themselves, figure it's worth asking.

Do the valves adjust easily like the B18B motors, or do you need to get the shims for it?

Quote:

Originally Posted by 4d_POWER

Replaced coils and plugs today. Plugs were black on the ends, also had some rust? on the ceramic.

Also adjusted the valves, many of the valves were tight. It was kinda scary opening the valve cover but went back together smoothly and fired right up after the 3 hour wait period.

One Note: I set the intake off to the side while working on the valves and noticed a puddle of oil on the ground underneath. Looked like about 1/2 a cup.
Only negative is the valves were gummed up pretty bad. Looked like 1/8-1/4 inch in places. Will have to look into a cleaning in the near future.

Wish I could have taken a good pic of the valves but couldn’t get the light inside the cylinder.

I used a 9/16 socket for the plugs, worked fine. It is a deep spark plug well though. I did have to use 2 short extensions. Place the socket and 1 extension into the well and then put 2nd extension in on top of that, no big deal. That’s just due to the cowl height restriction. It’s very workable though.

For the valve adjustment I used bent feeler gauges. The exhaust of #4 was the hardest to adjust, I just took a breath and was as patient as possible. No shims, just loosen bolt and adjust screw. I followed “KoolKevin1107” YouTube video for the adjustment process but used the 2015 specs of course.

Many owners and even dealerships think these motors only need adjustment when they make noise, but that is extremely false. Tight valves do not make noise and that's what the exhaust valves do on these motors.

Good for you for doing the adjustment and good luck with the carbon build up. Major downside to DI motors that many don't want to discuss.

Yes the carbon buildup on the valves freaked me out to be honest. Wish I had taken a good pic. It does have 130k. The throttle body was carboned up too but I was able to clean that up. Debating on a self brush/chemical clean or spending a little more for a walnut blast setup. Don’t know if it would be worth it for only using once or twice though. Found a great article here on the walnut process and have been watching some videos. https://www.northamericanmotoring.co...ss-3-27-13.pdf

For the valve adjustment I used bent feeler gauges. The exhaust of #4 was the hardest to adjust, I just took a breath and was as patient as possible. No shims, just loosen bolt and adjust screw. I followed “KoolKevin1107” YouTube video for the adjustment process but used the 2015 specs of course.

Update: Drove about ~50 more miles and came back with the exact same misfire codes cyl 1&3. (Brand new coils/plugs) Not noticeable to me while driving, but display lit up like a Christmas tree with CEL, steering, VSA, and low tire pressure lol.
Can’t stress enough how dirty the valves were so think I will try to do/find a valve cleaning service and see if that helps before looking into a fuel injector/pipe replacement. These motors are relatively easy to work on due to their size and the engine compartment. I do love this car with the 6 speed, room, and fuel mileage. It feels like it’s running fine so I’ll continue to drive it and tinker around and see if I can figure this out using this forum as a guide.

I am not sure if they are true misfires or just electrical spikes; or misfires that occur rarely enough not to bother with them. I lived with an occasional flashing CEL (flashing = misfire) on my suzuki esteem for years with no problems. Fuel economy was always great and had no complaints.

Before you move on to the $1000 injectors (they come as a set of 4 from what I gather), you can drive like this for a while and see how your fuel economy holds up.

Walnut blasting first, then went back over all valves with brushes and a can of CRC intake valve cleaner. I only have a small air compressor and I don’t think it was big enough for the job. It was able to remove 80%, The base of valve stem was really caked on, brushes and CRC worked using elbow grease to clean them good enough for me.